I am not sure I know all how a shunt trip breaker works, but the ones I am used to you use a control voltage signal to trip the breaker.

I have a customer ( and I don't have all the details) that has a tripping coil rated for 125VAC. Now he needs it to run on 125VDC for whatever reason. Is it possible to run a coil like that on either AC or DC? What will happen?

My customer came up with the idea to run a bridge rectifier in reverse to run this coil. I don't think there is any way this will work. A recitifer cuts the sine wave, right? to take the hz out of it? Running it in reverse, there is no way that it will be able to build a sine wave? He is sure that he has done this before, and it worked, but I don't see how.

My customer came up with the idea to run a bridge rectifier in reverse to run this coil. I don't think there is any way this will work. A recitifer cuts the sine wave, right? to take the hz out of it? Running it in reverse, there is no way that it will be able to build a sine wave? He is sure that he has done this before, and it worked, but I don't see how.

Any thoughts?

Is he joking?

Yeah it's diodes cutting the sine wave, in reverse the dc would see either a "brick wall" or a short circuit.

An inverter would do the trick, but that sounds more expensive/complicated than just getting the correct relay?

If you want happiness for an hour-take a nap. If you want happiness for a day-go fishing. If you want happiness for a month-getmarried. If you want happiness for a year-inherit a fortune. If you want happiness for a lifetime-help someone else.
----- Chinese Proverb

I don't mean to suggest this as any kind of practical solution but I believe you will find that an AC rated coil in a relay will operate successfully at a much lower DC voltage. You can play around with one in the lab and I believe that if you start very low with the DC and come up slowly, you will reach a voltage where the coil will attract the armature and not overheat.

This is not to recommend doing this. It might do if your life was at risk and you were stranded on a remote island with nothing but variable DC power but few other places.

If you disassemble an AC relay coil, you will find that it is simply a coil of wire (just like the DC version) but with a bronze shading ring around the nose of the magnetic core.

Without the shading ring, you would have a 60hz buzzer much like a motor starter with an AC coil and a broken shading ring. You have to replace the coil to get the starter to stop chattering but really, all you need to replace is the broken shading ring (comes with the new coil).

Of course, the AC coil is wound with different inductance and wire turns if the voltage was to be the same AC for DC in addition to the shading ring.